selftests/ublk: fix garbage output in foreground mode

Initialize _evtfd to -1 in struct dev_ctx to prevent garbage output
when running kublk in foreground mode. Without this, _evtfd is
zero-initialized to 0 (stdin), and ublk_send_dev_event() writes
binary data to stdin which appears as garbage on the terminal.

Also fix debug message format string.

Fixes: 6aecda00b7d1 ("selftests: ublk: add kernel selftests for ublk")
Signed-off-by: Ming Lei <[e-mail]>
Reviewed-by: Caleb Sander Mateos <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

tools/testing/selftests/ublk/kublk.c

···
 	}
 
 	ret = ublk_start_daemon(ctx, dev);
-	ublk_dbg(UBLK_DBG_DEV, "%s: daemon exit %d\b", ret);
+	ublk_dbg(UBLK_DBG_DEV, "%s: daemon exit %d\n", __func__, ret);
 	if (ret < 0)
 		ublk_ctrl_del_dev(dev);
 
···
 	int option_idx, opt;
 	const char *cmd = argv[1];
 	struct dev_ctx ctx = {
+		._evtfd         =       -1,
 		.queue_depth	=	128,
 		.nr_hw_queues	=	2,
 		.dev_id		=	-1,